This document describes methods for the determination of the dry matter content of lignins by oven-drying and freeze-drying. The methods are applicable to all types of lignins isolated from kraft, organosolv, soda, and sulfite pulping processes, and to lignin obtained by enzymatic or acid hydrolysis of biomass. However, the oven-drying method is not applicable to kraft lignins in the base form, also referred to as sodium form. Both methods are applicable only to lignins in the solid form.